This headline is deeply misleading. It is true that energy states are quantized. It does NOT follow that the transition between them is "instantaneous". The transition has always been known to be gradual, but the "gradualness" is not a smooth transition in the energy of the system, it's a smooth transition between being in one energy state to being in a superposition of two energy states to being entirely in the second energy state. That process plays out over (typically a very short but nonetheless non-zero) time. This has been known since the very beginning of QM.
What's news here is that this transition, which has always been predicted by theory, has been experimentally observed for the first time.
I have questions: you describe the change of states of particle as
"a smooth transition between being in one energy state to
being in a superposition of two energy states to being
entirely in the second energy state."
At the terminus of this transition, is the particle no longer in a superposition? IE there is now a 100% chance it's in the second state and 0% chance that it's in the original state?
If so, does that imply that the function of the particle's state (with respect to time) is discontinuous? Since there's a point at which it goes from being a superposition to exactly 0%.
I was extremely confused by the proposition because yes, it's known that energy states are quantized but I've never heard of any popular literature before suggesting the transition itself was quantized. Intuitively it doesn't even make sense that it could be quantized.
While not a perfect analogy, if I understand this properly, essentially if electrons jumping states were pitching in an unregulated game of baseball, the chances a pitcher will toss the ball increases as time goes on and previously we thought the ball just appeared over the plate instantaneously when that random time occurred.
But instead, while you still don't know when exactly, you do know there will be a wind up for the pitch before the ball is thrown, and we can see this windup, and we can time things to hit the ball, or shoot the pitcher with a blowdart and keep the pitch from happening.
So if there are systems in certain configurations to which this property is applicable to, and if we needed to keep things in that configuration until a time of our choosing, for instance if a state change occurs it would have cascading effects, we can do so.
As a quantum physicist: This might be an interesting experiment, but as far as the theory goes, this is exactly what is to be expected from standard quantum mechanics.
Quantum leaps being instantaneous would be a (possibly common) misconception.
The leap in a quantum leap is describing the notion of a discrete jump in measurement outcomes.
Okay, so you're a quantum physicist and you can answer my question!
My understanding of QM is that a quantum's system's state is suddenly and discontinuously changed by a measurement.
My understanding of this article is a bit confused, and I think that there are two possible things we could be seeing:
1. Quantum collapses of superpositions actually do take time ("This Changes Everything")
2. This particular quantum system is not actually being measured, but is oscillating in superposition in some odd way. ("Just a Particular System")
I guess I’m kind of confused on what the discovery is; we have a quantum system evolving unitarily from one state at t_0 to another state at t, and the probability of measuring the system in one of two discrete states changes continuously as well (despite the actual measurement outcome being discrete). I thought this has been known for a long time, implied by the time dependent Schrodinger equation, so I didn’t quite catch from the Quanta article what is new, mathematically. Can anyone clarify?
If you're a lay person like me and you want to make sense of this, read "Einstein’s Unfinished Revolution: The Search for What Lies Beyond the Quantum" by Lee Smolin. It was just published recently, and it anticipates this result!
A continuous jump means that the system travels coherently through the superposition of |0>+|1> through the jump, and other such a|0>+b|1> states for a^2+b^2=1. It isn't in 0, and then suddenly 1.
It’s a process of transition between two distinct states. Say a bit flips from 0 to 1; there is a short time period during which that bit is physically “in transition”, but it would be incorrect to say that the bit has a value of, say, 0.5 during the transition.
Also remember that quantum mechanics is a way to make statistical predictions of outcomes of certain experiments; it does not claim to explain what is actually happening underneath.
This is a common misconception. Quantum jump are jumps between two stable levels... there's nothing preventing "jumps" to unstable states, the particle just doesn't stay long in that specific state (although it can stay there long enough to be useful as in the case of two-photon absorption [0] and microscopy [1]).
If I understand it correctly, what this seems to imply is that it's not so much a (discontinuous) jump but rather a continuous(-ish) transition from one state to another.
Tangentially related request: I’m frequently very impressed with how many HN users seem to have a pretty solid grasp of physics (or maybe the right term is quantum mechanics?) and I’d love to be able to follow along but my science education more or else ended with high school. Could anyone recommend a good resource for someone with zero knowledge of this space to get very basic foundation?
It's not easy and you'd need to find problems to work, but http://www.feynmanlectures.caltech.edu is one source some people swear by. Others say it's too hard for a beginner text. I think both have a point, but it's free to see for yourself.
It's about gravity, not quantum field theory, but it's still very sound, very intuitive and explains the principles of the LIGO gravity wave detector. Also contains a bit of speculation about the culture and psychology of scientific creativity which I thought was great.
If you find a similar book on quantum phenomena, please post it!
Understanding Physics by Isaac Asimov is a great book that discusses Newtonian mechanics, thermodynamics, electromagnetism, and atomic physics. It presents it by discussing the history of the discoveries and experiments that advanced our understanding of the physics. The book is from 1966, so there have been numerous advances since, but it does go into a lot of detail of subatomic particles and radioactive decay. It is written to be understood by lay people and doesn't go very deep into the mathematics, which helps make it easier to understand.
The more I read about quantum mechanics the less i understand, and I'm absolutely unable to get into a proper learning path because it requires mathematics beyond my level and for which I'm not able to develop a taste on my own.
Of course I'm not interested in doing calculations but to appreciate quantum physics you have to know what the formalism behind are about and physicists are unable to explain it in simple terms for reasons I think I make out but can't properly formulate.
As an alternative path, Quantum Models of Cognition and Decision [1], may offer a less steep learning curve for the fact "you are the quantum system" and as such get to have actual experience with phenomena discussed in this book. To clear up the new-age vibe introduced in the last sentence, I think studying the maths through a phenomenon whose ambiguity is not questioned as a metaphysical abyss but is accepted as just being here in its mundane simplicity (semantic ambiguity in daily language use, that kind of thing) alleviates a lot of trouble in grasping what the maths mean in a physics course. Also the book is written for people coming from the fields related to psychology so it's a lot more approachable.
I just finished "Now: The Physics of Time" by Robert Muller. I have mixed feelings about the book, especially the chapters devoted to the author's interpretation of philosophy. I did enjoy hearing a history/overview of modern physics from someone in the field though, and it was a very approachable book. He was very clear about the open questions in quantum mechanics instead of hand-waving them away, which I appreciated.
I'm sure other books like Stephen Hawking's "A Brief history of Time" would be a good starting place too, but I can't speak to that one personally yet.
I wrote a comment one level above where I recommended "Einstein’s Unfinished Revolution: The Search for What Lies Beyond the Quantum" by Lee Smolin, and I thought I'd toss that in the ring here.
MIT OCW used to host their undergrad introduction to Physics lectures by Prof Walter Lewin which are pretty great. It was pulled down in 2014 but you'd definitely be able to find copies on Youtube.
"Natura Facit Saltus or No" was something Schrodinger wrote in 1952! (does nature jump or no?) Of course it's a continuous process, how else would water flow? As they mention in the article, here's the link to Schrodinger's paper "ARE THERE QUANTUM LEAPS?" https://academic.oup.com/bjps/article-abstract/III/11/233/14...
> "The strategy reveals that quantum measurement is not about the physical perturbation induced by the probe but about what you know (and what you leave unknown) as a result. “Absence of an event can bring as much information as its presence,” said Devoret."
If a quantum system is going to transition between two states that have different energy, would we not expect it to take a time specified by the Heisenberg Uncertainty Principle? If the change in energy is delta E, would we not expect the transition to take delta T = h bar/delta E?
> would we not expect it to take a time specified by the Heisenberg Uncertainty Principle?
There isn't actually an energy-time version of the uncertainty principle, at least not the simple one you're assuming here, although many pop science presentations talk as if there is. A good article discussing this is here:
For a quantum system transitioning between states, the probability of transition in general will vary as a function of time; how it varies depends on the specific state of the system. There is no general rule that relates the expected transition time to the change in energy. (Note also that not all transitions are between energy eigenstates.)
No, the time to complete one transition is the inverse of Rabi frequency, which is actually determined by strength of external field and nature of the transition (its dipole moment matrix elements), see e.g. https://en.wikipedia.org/wiki/Rabi_frequency
If I am understanding the article correctly, there is no hidden variable implied. Quantum physics claims changes are random, with nothing precise and determinate underneath that causes this.
Think of the example of flipping a coin. It's random, but for each flip if you had exact data for the movement of the coin as it left your hand, you would presumably be able to predict if it would land heads or tails. Quantum physics claims that for events at the quantum level, there is nothing definite underneath that determines what will happen, it is just fundamental randomness. The hidden variable idea is that there is something definite underneath, we just haven't discovered it yet.
What the experiment seems to have found is only that the probability of an event occurring changes smoothly over time from 0 to 1, not that there is some underlying exact cause for what the probability is at a given point in time.
Amazing. What is the energy of the system while it's in transition? I guess they're arguing superposition of 1 and 0, continuously sliding to a higher likelihood with time. I mean, eventually a photon is emitted, and that can't be continuous. I guess I'll have to read the preprint.
By which frame of reference? I never understood the language around "instantaneous". Isn't simultaneity relative? So that where one frame of reference says two events are simultaneous, there or others that say they are not?
The old quantum theory was developed in non-relativistic setting, so this was not a concern. But you are right, relativity complicates lots of things in quantum theory, including the idea of "instantaneous" quantum jumps. In relativity, if some event is to be universally instantaneous, then it has to happen at a single point of space. Which is possible with point particles, but then you get the problem how those point particles can find each other to interact at a single point so often as measured cross sections indicate... perhaps they are not exactly points, but waves, but then we can't have instantaneous events, the event has to happen to the wave in big region of space where simultaneity is relative.
Simultaneity is only relative when events A and B are far enough apart that it would have been impossible for light to get from one to the other between the two events. When there is a single location, it's objective whether something has zero or nonzero duration.
And while observers disagree on their personal measurements of duration, they will always agree about what a clock sitting at the location will measure.
“Another text saying that the founding fathers of quantum mechanics were not only wrong but idiots, as some current geniuses revealed. In reality, it's the other way around, of course. [...] I don't think it makes sense for me to discuss the paper and Ball's summary more deeply. One would have to correct every sentence that is wrong or at least misleading – which is basically every sentence both in Ball's text as well as the text in Nature.“
[+] [-] lisper|6 years ago|reply
What's news here is that this transition, which has always been predicted by theory, has been experimentally observed for the first time.
[+] [-] posix_compliant|6 years ago|reply
If so, does that imply that the function of the particle's state (with respect to time) is discontinuous? Since there's a point at which it goes from being a superposition to exactly 0%.
[+] [-] soulofmischief|6 years ago|reply
I was extremely confused by the proposition because yes, it's known that energy states are quantized but I've never heard of any popular literature before suggesting the transition itself was quantized. Intuitively it doesn't even make sense that it could be quantized.
Was this a popular scientific opinion?
[+] [-] molticrystal|6 years ago|reply
But instead, while you still don't know when exactly, you do know there will be a wind up for the pitch before the ball is thrown, and we can see this windup, and we can time things to hit the ball, or shoot the pitcher with a blowdart and keep the pitch from happening.
So if there are systems in certain configurations to which this property is applicable to, and if we needed to keep things in that configuration until a time of our choosing, for instance if a state change occurs it would have cascading effects, we can do so.
[+] [-] joycian|6 years ago|reply
[+] [-] SubiculumCode|6 years ago|reply
[+] [-] inflatableDodo|6 years ago|reply
[+] [-] trurl42|6 years ago|reply
Quantum leaps being instantaneous would be a (possibly common) misconception.
The leap in a quantum leap is describing the notion of a discrete jump in measurement outcomes.
[+] [-] neaanopri|6 years ago|reply
My understanding of QM is that a quantum's system's state is suddenly and discontinuously changed by a measurement.
My understanding of this article is a bit confused, and I think that there are two possible things we could be seeing: 1. Quantum collapses of superpositions actually do take time ("This Changes Everything") 2. This particular quantum system is not actually being measured, but is oscillating in superposition in some odd way. ("Just a Particular System")
Which case is it?
[+] [-] Xcelerate|6 years ago|reply
[+] [-] maxharris|6 years ago|reply
https://www.penguinrandomhouse.com/books/316818/einsteins-un...
[+] [-] outlace|6 years ago|reply
[+] [-] joycian|6 years ago|reply
How is this in any way consistent with the rest of quantum mechanics?
Edit: I don't mean to sound snide, I am genuinely confused about what this experiment means.
[+] [-] gaze|6 years ago|reply
[+] [-] trevyn|6 years ago|reply
Also remember that quantum mechanics is a way to make statistical predictions of outcomes of certain experiments; it does not claim to explain what is actually happening underneath.
[+] [-] Anon84|6 years ago|reply
If I understand it correctly, what this seems to imply is that it's not so much a (discontinuous) jump but rather a continuous(-ish) transition from one state to another.
[0] https://en.wikipedia.org/wiki/Two-photon_absorption
[1] https://en.wikipedia.org/wiki/Two-photon_excitation_microsco...
[+] [-] elliekelly|6 years ago|reply
[+] [-] abecedarius|6 years ago|reply
https://www.amazon.com/Thinking-Physics-Understandable-Pract... is not free, but also excellent and gentler.
[+] [-] wwarner|6 years ago|reply
It's about gravity, not quantum field theory, but it's still very sound, very intuitive and explains the principles of the LIGO gravity wave detector. Also contains a bit of speculation about the culture and psychology of scientific creativity which I thought was great.
If you find a similar book on quantum phenomena, please post it!
[+] [-] orbifold|6 years ago|reply
[+] [-] bradyd|6 years ago|reply
[+] [-] GorgeRonde|6 years ago|reply
Of course I'm not interested in doing calculations but to appreciate quantum physics you have to know what the formalism behind are about and physicists are unable to explain it in simple terms for reasons I think I make out but can't properly formulate.
As an alternative path, Quantum Models of Cognition and Decision [1], may offer a less steep learning curve for the fact "you are the quantum system" and as such get to have actual experience with phenomena discussed in this book. To clear up the new-age vibe introduced in the last sentence, I think studying the maths through a phenomenon whose ambiguity is not questioned as a metaphysical abyss but is accepted as just being here in its mundane simplicity (semantic ambiguity in daily language use, that kind of thing) alleviates a lot of trouble in grasping what the maths mean in a physics course. Also the book is written for people coming from the fields related to psychology so it's a lot more approachable.
[1] http://bacon.umcs.lublin.pl/~lukasik/wp-content/uploads/2010...
[+] [-] plokiju|6 years ago|reply
I'm sure other books like Stephen Hawking's "A Brief history of Time" would be a good starting place too, but I can't speak to that one personally yet.
[+] [-] blojayble|6 years ago|reply
[+] [-] jcroll|6 years ago|reply
I spent a couple months going through its backdated articles and it was a great read
[+] [-] maxharris|6 years ago|reply
[+] [-] thelastbender12|6 years ago|reply
[+] [-] codekilla|6 years ago|reply
[+] [-] sova|6 years ago|reply
[+] [-] amatus|6 years ago|reply
[+] [-] unknown|6 years ago|reply
[deleted]
[+] [-] rotrux|6 years ago|reply
> "The strategy reveals that quantum measurement is not about the physical perturbation induced by the probe but about what you know (and what you leave unknown) as a result. “Absence of an event can bring as much information as its presence,” said Devoret."
[+] [-] AnimalMuppet|6 years ago|reply
[+] [-] pdonis|6 years ago|reply
There isn't actually an energy-time version of the uncertainty principle, at least not the simple one you're assuming here, although many pop science presentations talk as if there is. A good article discussing this is here:
http://www.math.ucr.edu/home/baez/uncertainty.html
For a quantum system transitioning between states, the probability of transition in general will vary as a function of time; how it varies depends on the specific state of the system. There is no general rule that relates the expected transition time to the change in energy. (Note also that not all transitions are between energy eigenstates.)
[+] [-] effie|6 years ago|reply
[+] [-] xwdv|6 years ago|reply
[+] [-] pontifier|6 years ago|reply
There seems to be some sort of "hidden variable" there... can anyone explain it?
[+] [-] woodandsteel|6 years ago|reply
What the experiment seems to have found is only that the probability of an event occurring changes smoothly over time from 0 to 1, not that there is some underlying exact cause for what the probability is at a given point in time.
[+] [-] coldcode|6 years ago|reply
[+] [-] wwarner|6 years ago|reply
[+] [-] unknown|6 years ago|reply
[deleted]
[+] [-] bladedtoys|6 years ago|reply
By which frame of reference? I never understood the language around "instantaneous". Isn't simultaneity relative? So that where one frame of reference says two events are simultaneous, there or others that say they are not?
[+] [-] effie|6 years ago|reply
[+] [-] Dylan16807|6 years ago|reply
And while observers disagree on their personal measurements of duration, they will always agree about what a clock sitting at the location will measure.
[+] [-] kgwgk|6 years ago|reply
https://motls.blogspot.com/2019/06/experimenters-and-especia...
[+] [-] deepspace|6 years ago|reply
https://rationalwiki.org/wiki/Lubo%C5%A1_Motl
[+] [-] drenvuk|6 years ago|reply
[+] [-] Simon_says|6 years ago|reply